Permanent magnetic alloy composed of platinum,gold and iron

ABSTRACT

A PERMANENT MAGNETIC ALLOY, COMPRISING: 15-40 ATOMIC PERCENT OF PLATINUM, 5-35 PERCENT OF GOLD AND 40 ATOMIC PERCENT OF IRON.

July 6, 1971 SHQTARQ s zu ETAL 3,591,373

PERMANENT MAGNETIC ALLOY COMPOSED 0F PLATINUM. GOLD AND IRON Filed Oct. 7, 1968 /0Pt /5Pt 20/32 United States Patent Office 3,591,373 Patented July 6, 1971 Japan Filed Oct. 7, 1968, Ser. No. 765,604 Int. Cl. C22c 5/00; HOlf 1/04 US. Cl. 75-172 4 Claims ABSTRACT OF THE DISCLOSURE A permanent magnetic alloy, comprising: -40 atomic percent of platinum, 5-35 atomic percent of gold and atomic percent of iron.

This invention relates to improvements in and relating to a permanent magnetic alloy. More specifically, it relates to a permanent magnet which is highly powerful, lighter in its weight and smaller in its size when compared with conventional comparative permanent magnets having equal performance, and highly adapted for use in the manufacture of magnetic elements for precision small devices and instruments such as electric watches, hearing aids, micromotors, exposure meters, as well as larger appliances such as travelling wave tubes for satellite telecommunication, and the like.

Among other known permanent magnet materials platinum cobalt alloy is known as the most powerful one. This alloy not only has powerful and efiicient magnetic properties, but also it is characterized by its ready fabrication characteristics and easy machinability, for instance, with respect to rolling, turning and the like. Therefore, this material finds its broad use in the manufacture of miniature permanent magnets for use in small precision machines and elements such as electric watches.

The platinum-cobalt alloy has the following two appreciable drawbacks. The most predominant one resides in its amazingly high production cost on account of its high content of platinum, i.e., as high as 77 wt. percent. Another drawback resides in its heavy density such as about 15.5 grs. per cub. centimeter, caused again by its high content of platinum as above specified. As is commonly known, the platinum-cobalt alloy provides most powerful magnetic properties, especially when it forms a super lattice which develops by a one-to-one alloying combination of platinum and cobalt atoms. This optimum alloy has thus such a chemical composition: atomic percent of platinum and 50 atomic percent of cobalt, showing therefore 77 wt. percent platinum and 23 wt. percent of cobalt. A marked deterioration of magnetic properties of the alloy will be invited when a reduction of the platinum content is used to reduce the high manufacturing cost and the inherent high density. Therefore, attempts in this respect are not favorable in practice.

Platinum-iron alloy may be used for similar purposes. It was believed among those skilled in the art that this kind of magnetic alloy has considerably inferior magnetic performances relative to platinum-cobalt alloy. It was found, however, as disclosed in our prior US. application Ser. No. 465,894 filed June 22, 1965, now US. Pat. 3,444,012, dated May 13, 1969, that platinum-iron alloy may represent similar favorable magnetic properties as those of platinum-cobalt alloy by subjecting it in addition to conventional heat treatment to specific plastic deformation. This proposed alloy is also defective in its high productive cost and high density of about 15.0 grs. per cub. centimeter. The necessary plastic deformation confines the alloy to limited practical usage.

It is therefore the main object of the invention to provide a new platinum alloy capable of providing superior results as compared to the platinum cobalt alloy in its magnetic properties.

It is a further object of the invention to provide a new platinum alloy which is lower in its production cost and smaller in its density as compared with platinum-cobalt alloy.

Commercially available magnetic materials contain frequently a considerable amount of cobalt. Among others, the platinum-cobalt alloy, Alnico, (Fe-Ni-Al-Co alloy) and Vicalloy (Fe-Co-V alloy) may be referred to. The cobalt may turn into a dangerous radioisotope having a long half life, and thus, the platinum-cobalt alloy and the like cobalt-containing alloys cannot be utilized in various appliances attached to an atomic pile.

An additional object of the present invention is to provide a powerful permanent magnetic material which does not contain any appreciable content of cobalt as its alloying component.

These and further objects, features and advantages will become more apparent upon a reading of the following detailed description of the invention by reference to the sole accompanying drawing which constitutes part of the present specification, as well as several numerical examples to be given hereinafter.

The drawing shows a ternary composition diagram of the platinum-gold-iron magnetic alloy in accordance with the present invention, the chemical composition being shown in atomic percentages.

In this diagram, small circles represent respective composition of specimens examined, and numerals given within these circles each represent the corresponding number of the numerical Examples 1-8 to be set forth. In this diagram, the energy product which is normally expressed by Bd Hd, being one of the most important properties of the permanent magnetic alloy obtained in accordance with the invention, is illustrated by four closed curves or contour lines, numerals 10, 8, 6, and 4 given thereon representing each the energy product in MGOe which is an abbreviation of mega gauss oersteds. The hatched range corresponds to alloying percentages disclosed in the appended claims.

In the following, several preferred numerical examples illustrative more specifically of the invention will be described in detail.

EXAMPLE 1 grs. of commercially available pure metal powder, 200 mesh, of Pt, Au and Fe were mixed thoroughly together in an overall atomic ratio of 35:20:45 and pressed into solid cylinders, height 10 mm., dia. 10 mm., under a pressure of 20 tons per square centimeter.

These were then sintered at the temperature of 1,100 C. for 5 hours. This atomic ratio is represented diagramatically on the drawing at 1. Then, the cylinder was heated at 1,000 C. for an hour and cooled down to room temperature at a cooling rate of 50 C./min. This specimen was tested for its magnetic properties. The test results were highly superior as shown in the first line of Table 1.

EXAMPLE 2 A powder mixture of Pt, Au and Fe in an atomic ratio of 30:25:45 was shaped into solid cylinders as before. These cylinders were then heated at 1,000 C. for an hour, cooled down to room temperature at a rate of 200 C./min. and finally aged at 650 C. for an hour. The resultant magnetic properties are shown in the second line of Table 1. Also, see 2 on the drawing.

EXAMPLE 3 A powder mixture of Pt, Au and Fe in an atomic ratio of 35:15:50 was shaped into a rigid cylinder as before, which cylinder was then heated at 1,100 C. for an hour, oil quenched and finally aged at 700 C. for minutes. The resultant magnetic properties are shown in the third line of Table 1. Also, see 3 on the drawing.

EXAMPLE 4 A powder consisting of Pt, Au and Fe in an atomic ratio of :25:50 was shaped into solid cylinders as before, which cylinders were then heated to 1,100 C. for an hour and thrown into a molten salt bath kept at 650 C. This final heat treatment extended for an hour. The resultant magnetic properties are shown in the fifth line of Table 1. See also 5 on the drawing.

EXAMPLE 6 A powder mixture consisting of Pt, Au and Fe in an atomic ratio of 20:30:50 was shaped into a solid cylinder as before, which cylinder was then heated to 1,000 C. for an hour and thrown into a molten salt bath kept at 650 C. This final heat treatment extended for two hours.

The resultant magnetic properties are shown in the sixth line of Table 1. See also 6 on the drawing.

EXAMPLE 7 A powder mixture consisting of Pt, Au and Fe in an atomic ratio of :10:55 was shaped into solid cylinders as before, which cylinders were then heated to 1,100 C. for an hour, oil quenched and finally aged at 725 C. for 15 minutes. The resultant magnetic properties are shown in the seventh line of Table 1. See also 7 on the drawing.

TABLE 1 Properties Composition by atomic percent 4 at 700 C. for 30 minutes. The magnetic properties of the thus obtained alloy are shown in line 10 of Table 1. See also 10 on the drawing,

Including the foregoing experiments, we prepared about 120 alloys and made various heat treatments thereon from which the chart shown on the drawing was plotted. As seen from the foregoing Examples 1-10, the preparation of these alloys were carried into effect by the powder metallurgical process. It should be however expressly understood that the invention may be carried about through the way of the conventional melting proceis, as will be seen from the following additional examp es.

EXAMPLE 1 1 About 100 grs. of the alloying composition set forth in the foregoing Example 4, were melted in an H.F. induction furnace at about 1,700 C., and cast into an ingot, 15 mm., which was then swaged and cut into several solid cylinders, each 10 mrn.q5 and 10 mm. long. These specimens were subjected to heat treatment set forth in the same example. The resultant properties were:

Br=8,300 gausses; Hc=3,500 oersteds; (Bd.Hd)=10.8 MGOe; Density:15.0 grs./cc.

EXAMPLE 12 A similar alloying material set forth in the foregoing Example 10 was prepared and melted at 1,700 C. Further processing was carried out as in Example 10. The resultant properties were:

Br=9,400 gausses; Hc=3,l00 oersteds; (Bd.Hd) =10.4 MGOe; Density=14.4 grs./cc.

The following Table 1 shows the resulted magnetic performances of several alloys which were prepared in the foregoing Examples 1-10. As seen, the obtained properties were comparative to those of a representative platinum-cobalt alloy; Platinax II, manufactured by Johnson Matthey Co. Ltd., London.*

(Bd.Hd) Density,

--- Br, He,

Pt Pd Au Fe Ni Co gauss oersted MGOe g a 1O 5 9, 000 2, 300 9.8 14. 0 Platinax II- 6, 480 4, 600 9. 4 l5. 5

EXAMPLE 8 A powder mixture consisting of Pt, Au and Fe in an atomic ratio of 30:15:55 was shaped into solid cylinders as before, which cylinders were then heated to 1,100 C. for an hour, oil quenched and finally aged at 725 C, for 5 minutes. The resultant magnetic properties are shown in the eighth line of Table 1. See also 8 on the drawing.

EXAMPLE 9 An intimate powder mixture of Pt, Au, Fe and Co in an atomic ratio of 30:15:5015 was shaped under pressure into solid cylinders as before, which cylinders were heated at 1,100 C. for an hour, oil quenched and finally aged In the following, a brief review on the superior magnetic properties of the permanent magnetic alloy prepared in accordance with the new teaching of the invention will be made.

Magnetic performance As seen especially from the foregoing Examples 4, 8 and 10, the magnetic alloy according to the invention may have a higher energy product which means a considerable progress in the art and is highly valuable in the manufacture of small powerful magnetic elements.

Manufacturing costs As seen from Table 1, the platinum content is small in comparison with the conventional platinum-containing magnetic alloy such as Platinax II which results in a corresponding reduction in the manufacturing cost.

Density The density of the alloy according to this invention is considerably lower than that of the conventional platinumcontaining alloys.

*Platinax II: See, Platinum Metal Review, vol. 8, pp. 82-90, 1964.

Therefore, the weight of the magnet prepared from the new alloy is considerably lighter than conventional alloy with equal magnetic performance, which means a considerable advantage in the manufacture of moving magnet type instruments or various magnetic appliances attributed to satellites.

Non-radioactivity The magnetic alloy according to this invention does not contain any appreciable content of cobalt which may turn into a harmful radioisotope, when excepting the foregoing Examples and 12, thus providing a favorable feature in the art, as was already referred to.

As seen especially from thedrawing, the platinumgold-iron alloy proposed by the present invention provides superior magnetic properties with a considerably broad range of alloying percentages. This means that the new alloy is rather non-sensitive to its specific composition and any one of or any combination of specific additives such as CO, Ni, Cu, Pd, Ag, Rh, Ir and the like may be added in minor amounts such as 0.15 atomic percent in the former instance, and 0.1-10 atomic percent in the latter instance, without any appreciable reduction in the desired magnetic properties. In this respect, reference may be had to the foregoing Examples 9 and 10. Therefore, these modified alloys should be covered by the true scope and spirit of the present invention as set forth in the appended claims.

As clearly seen from the foregoing, especially from Examples 4 and 8, the most advantageous and superior magnetic performances are attained with the embodiments which have been set forth in these specific examples. However, when considering the eoonomic advantage hereinbefore set forth, those alloy embodiments of rather lower performance which were given in the foregoing Examples 5, 6 and 9 are also valuable from the practical point of view.

Although in the foregoing, only a limited number of embodiments have been shown and described, it should be expressly understood that various and different modifications will easily occur to those skilled in the art when reading through the foregoing disclosure of the present specification, and these modifications and changes should be included in the true scope and spirit of the invention so far as they fall within the range set forth in the appended claims.

What we claim is:

1. A permanent magnetic alloy consisting essentially of 15-40 atomic percent of Pt, 5-35 atomic percent of Au and -60 atomic percent of Fe.

2. A permanent magnetic alloy as set forth in claim 1, further comprising 0.1-5 atomic percent of a member selected from the group consisting of Co, Ni, Cu, Pd, Ag, Rh and Ir.

3. A permanent magnetic alloy as set forth in claim 1, further comprising 0.1-10 atomic percent of a combination of any two or more members selected from the group consisting of Co, Ni, Cu, Pd, Ag, Rh and Ir.

4. A permanent magnetic alloy, as set forth in claim 1, containing substantially no Co.

References Cited UNITED STATES PATENTS 2,780,543 2/1957 Schneider et a1 -165 3,140,941 7/1964 Walter 75-122 3,206,337 9/1965 Walmer 148-31.57 3,440,012 5/1969 Shimizu et. a1. 148101 L. DEWAYNE RUTLEDGE, Primary Examiner E. L. WEISE, Assistant Examiner US. Cl. X.R. 

